1. Field of the Invention
The present invention relates to a multimedia data transmission technique.
2. Description of the Related Art
Conventionally, a description method called a URI for identifying resources such as files on a network is defined by the specifications of RFC3986 disclosed by IETF. According to the specifications, the user of the URI can express a secondary resource such as partial data of a main resource by adding a description called a fragment identifier to a portion of the URI.
In addition, W3C is defining the specifications of a media fragment URI for expressing data obtained by splitting multimedia data such as a movie in accordance with the time, coordinates, and track type (for example, an image, sound, or subtitle) by using the fragment identifier.
According to the specifications, when acquiring a movie from a movie distribution apparatus, a movie reproduction terminal apparatus as described in Japanese Patent Laid-Open No. 2001-204001 can designate a part of the movie as an acquisition target by using the URI containing the fragment identifier.
When a resource as an acquisition target exists on a Web server, HTTP/1.1 whose specifications are disclosed by RFC2068 is often used as a communication protocol. HTTP/1.1 defines an HTTP compression encoding scheme, and can suppress the network load by decreasing the data size by compressing a resource having a compression effect. Note that the specifications of the HTTP compression encoding scheme define the use of compression schemes such as “deflate”, “compress”, and “gzip”.
In a Web system including a Web server holding movie data and a network terminal that uses moving data, the terminal sometimes uses only partial data of a movie such as a subtitle track.
For example, the terminal selects or excludes a movie including a specific keyword in a subtitle from a plurality of movies on the Web server, or presents the start portion of a subtitle of each movie as an index to the user.
As a simple method of implementing these uses, it is possible to allow the terminal to acquire all movie data from the Web server, and separate the necessary data portion such as a subtitle track by an application called a splitter corresponding to the format of each movie data.
Unfortunately, when the storage capacity for storing the whole movie data is small or the resources such as the computability for operating a plurality of splitters are little, for example, when the terminal is a small apparatus, the processing speed decreases when implementing the above-mentioned uses.
On the other hand, the Web server often has more resources than those of the terminal, the problem of the processing speed as described above can be solved by using a method by which the terminal requests the Web server for partial data of a movie, and the Web server splits the data. A procedure of performing this method is that the terminal notifies the Web server of a necessary data range by using a description method such as the media fragment URI, and acquires the corresponding partial data from the Web server. In this procedure, the Web server transmits the partial data requested by the terminal as data having the same media type as that of the unsplit movie data.
Since movie data is generally already compressed, the compression effect in transmission is small, so data having the media type of movie data is transmitted without HTTP compression. However, many movie data such as MPEG-4 file data have a container form including a plurality of tracks. When movie data like this is split in accordance with the track type, partial data sometimes has a compression effect.
When transmitting partial data from the Web server, however, the data is transmitted as it is uncompressed regardless of its compression effect. This makes the network load impossible to reduce.